The present invention relates to the field of measuring devices and a method and apparatus for measuring items. More particularly, the present invention relates to a method and apparatus for confirming that items in a universe of items, such as pipes, fall within specified tolerances. In an alternative embodiment the present invention relates to selecting a best fit between various items from a universe of items, such as a universe of pipes.
When selecting two pieces of pipe for joining from a universe of pipe it is desirable to select to pieces which fall within acceptable tolerances. For example, it may be desirable to ensure that the largest dimensional difference between two items to be joined is less than a set amount (e.g, less than 0.5 millimeters). It may also be desirable that, for a universe of items to be joined end to end, for those items which fall below the set largest dimensional difference, that the items to be joined be selected so that the dimensional differences between any two items be minimized. Minimizing the dimensional differences allows for the most favorable conditions to join items and minimizes stress concentrators at the joining points thereby increasing the factor of safety at the joints and reducing the risk of failure at a future point.
During the process selecting pipes to be joined from a universe of pipes, it is desirable to measure the pipe to ensure compliance with predetermined tolerances for quality control. Of particular concern are the dimensions of the pipe at its end that will form a juncture with a second piece of pipe. These measurements have traditionally been performed with simple “go/no-go” gauges, or at times with calipers.
Go/no-go gauges are mechanical articles of a fixed size which, when inserted, or attempted to be inserted, into a pipe will fit properly or not, indicating whether the tested pipe is acceptable. These gauges check the minimum or maximum dimensions at certain critical points in the ends. Calipers provide actual dimensions, but it is time consuming and subject to human error to measure the pipe with calipers or any other standard measuring device.
For a universe of pipes it would be desirable to have a system for taking various measurements of each pipe and automatically determining which pipes best fit each other and determine any pipe sections that need to be machined in order to bring the pipe into conformity with specified tolerances.
As with any manual system, human error is pervasive. An automated measuring system is needed. Some automated contact systems are available. Such systems typically use some form of linear variable differential transformer or linear potentiometer, both of which require a sensor to touch the surface of the unit under test. However, the interior surface of a pipe may be abrasive, and in a volume manufacturing process the sensor would wear out in an unacceptably short time. Using such contact sensors therefore would increase maintenance costs and process down time) while decreasing the reliability, and over time, the precision of the measurement system. Moreover, the range of most contact sensors is rather limited and is insufficient to measure large diameter pipe. As discussed previously, there are several points of interest on the pipe or tubular end. To measure multiple points with a contact system, the sensor would need to be removed from the surface, repositioned to the new location, and then placed in contact with the surface again.
Thus, there exists a need for a method and apparatus for selecting the best fit of two items between a universe of items along with a method for determining whether an item falls within specified tolerances; that will perform the selection process in a fast manner and minimize human error in making such determinations.
The following U.S. patents are incorporated herein by reference: U.S. Pat. No. 6,289,600.
While certain novel features of this invention shown and described below are pointed out in the annexed claims, the invention is not intended to be limited to the details specified, since a person of ordinary skill in the relevant art will understand that various omissions, modifications, substitutions and changes in the forms and details of the device illustrated and in its operation may be made without departing in any way from the spirit of the present invention. No feature of the invention is critical or essential unless it is expressly stated as being “critical” or “essential.”